The present invention relates generally to ignition systems for rotary piston engines, and more particularly the invention relates to a control system for controlling the supply of power to the glow plug included in the ignition means of such ignition system.
While the rotary piston engine is basically a spark ignition engine, by virtue of its structure, it is possible to accomplish continuous ignition of the engine by means of a glow plug. In the case of a rotary piston engine whose ignition means consists of a glow plug which is mounted at a position 1/4 from the forward end of the combustion chamber which is at the top dead center on the compression stroke, it is possible to ensure considerably improved fuel consumption and reduced exhaust emissions as compared with the ordinary rotary piston engine.
In this case, according to what have been confirmed by the inventors, in order that the mixture may be ignited by the glow plug, the surface temperature of the glow plug must be over 900.degree. C. On the other hand, in consideration of the durability of the glow plug itself, it is desirable to hold the surface temperature of the glow plug below 1100.degree. C. and thus it is important to hold the surface temperature of the glow plug within a range from 900.degree. to 1100.degree. C. However, the required power supply to the glow plug for holding its surface temperature within such a range cannot be constant. In other words, the surface temperature of the glow plug is affected not only by the heat generation of the glow plug itself which is dependent on the supplied power but also by the amount of heat exchanged between the glow plug and the combustion gases in the combustion chamber. As a result, if the amount of power supply is preset so that the surface temperature of the glow plug becomes proper when the amount of heat radiation of the combustion gases is small as during the periods of high speed and low load operation, this poses a problem that such burning losses as a breakage in the heating coil, melting loss of the casing and the like will be caused by the glow plug during the periods of low speed operation or high load operation where the amount of heat radiation of the combustion gases is large.